1. Field of the Invention
This invention relates to a semiconductor laser array device which emits high-output power laser light with a far-field pattern having a single peak.
2. Description of the Prior Art
Semiconductor laser devices which are useful as light sources of laser discs, space communication systems, etc., must produce high-output power. However, conventional semiconductor laser devices would produce about 80 mW at their best in view of practical use so long as a single filament structure is adopted thereto. Semiconductor laser array devices, in which a plurality of lasing filaments are disposed in a parallel manner on a single substrate, have been studied.
FIG. 7 shows a conventional semiconductor laser array device in which a plurality of lasing filaments 1 are disposed in a parallel manner on a single substrate to achieve an optical phase coupling between the adjacent filaments. When gain is uniformly applied to each of the lasing filaments, the semiconductor laser array device tends to oscillate in a 180.degree. phase-shift mode indicated by reference numeral 3 in FIG. 7, rather than in a 0.degree. phase-shift mode indicated by reference numeral 2 in FIG. 7. This is based on the fact that the optical field distribution is in accord with the gain distribution in the 180.degree. phase-shift mode rather than in the 0.degree. phase-shift mode, resulting in high oscillation gain.
The far-field pattern of laser light in a 0.degree. phase-shift mode attained by a conventional semiconductor laser array device exhibits a single peak as shown in FIG. 6(a), so that the laser light can be concentrated into a single spot fashion by means of an optical lens, while the far-field pattern of laser light in a 180.degree. phase-shift mode attained by a conventional semiconductor laser array device exhibits dual peaks as shown in FIG. 6(b), so that the laser light cannot be concentrated into a single spot fashion by means of any optical lens and is useless as a light source for optical discs, etc. Therefore, the optical phase shift between the adjacent filaments of a semiconductor laser array device is required to be 0.degree..